The present invention relates to a method to assign upstream timeslots to a network terminal, as defined in the preamble of claim 1, a network terminal adapted to perform this method, as defined in the preamble of claim 13, and a medium access controller adapted to perform this method, as defined in the preamble of claim 17.
Such a method, network terminal and medium access controller are already known in the art, e.g. from the European patent specification EP 0 544 975 B1 xe2x80x9cTime slot management systemxe2x80x9d. Therein, a time slot management system is described, being part of a communication system including a main station coupled to each of a plurality of substations or user stations in a point-to-multipoint way, via the cascade connection of a common transmission link and an individual user link. The medium access controller of the present invention thus corresponds to the time slot management system of the prior art document, the network terminals to the substations or user stations, and the central station to the main station of this prior art document. The prior art time slot management system, includes a conversion and transmission means which is adapted for generating grants associated to the substations for downstream transmission to them. Upon receipt of the associated grant by the substations, these are then allowed to transmit a predetermined amount of upstream data packets to the central station. The prior art conversion and transmission means corresponds to the grant generation means of the present invention. In the prior art system, the rate with which succeeding occurrences of network terminal grants are generated is directly proportional to bandwidth information earlier transmitted upstream by the user stations, for instance the peak rate at which the user station intends to perform upstream packet transfer.
A drawback of the prior art system however is that it does not differentiate among different service categories pertaining to different packet or bitstreams the network terminals want to transfer upstream to the central station. Furthermore, to guarantee that each user station of the prior art system, can transfer its upstream data, the information related to the bandwidth requested by each user station or network terminal, usually corresponds to a peak cell rate, being the maximum rate at which this network terminal needs to upstream transfer its data packets. This prior art system is therefore functioning properly as long as the network terminals indeed have to transfer upstream bitstreams pertaining to a service category for which only a peak cell rate is specified, for instance the constant bit rate category as specified by the ATM Forum specification AF-TM-0056.000 dated April 1996 in case the bitstreams consist of ATM streams. In case however a network terminal intends to send packets pertaining to another, for instance the so-called xe2x80x9cbest effortxe2x80x9d service category such as the unspecified bit rate service category, described in the same ATM Forum specification, reserving a maximum peak cell rate equivalent bandwidth during a certain time period, while the packets are only to be transferred at irregular instances in short bursts, seriously underutilises the capacity of the upstream link. At the some time, this may result in a high call blocking probability since the aggregate of the peak cell rates of the supported connections cannot exceed the available upstream capacity of the common transmission link, which was necessary to secure the correct operation of the prior art time slot management system.
An object of the present invention is to provide a method, a network terminal, and a medium access controller of the above known type but which allows to differentiate amongst different types of service categories pertaining to several bitstreams or connections to be upstream transmitted from this network terminal to the central station, and which at the same time, aims at a more efficient use of the capacity of the common upstream transmission link.
According to the invention, this object is achieved due to the fact that said method is further adapted as is described in the characteristic part of the first claim, that said network terminal is further adapted as described in the characteristic part of claim 13 and that said medium access controller is further adopted as described in the characteristic part of claim 17.
In this way, differentiation between different service categories is first realised within said network terminal by sorting or classifying, and temporarily storing the data packets to be upstream transmitted in different storage queues, each respective storage queue corresponding to a respective service category. This sorting is for instance based on header information, as will be explained more into detail in a following paragraph. Secondly, also the grant generation means is adapted to generate differentiated grants with respect to each different service category.
Furthermore, the grant rate associated to a particular storage queue is thereby not only determined from the parameters associated to this storage queue, but is also based upon at least one other parameter related to another storage queue within any network terminal of the communications network. This leads to a better partitioning of the available upstream bandwidth of the common transmission link since the upstream packet transmission rate will now be modulated, based on parameters associated to two competing bitstreams of which the packets are stored in these two storage queues.
These competing bitstreams can be upstream transmitted from the same network terminal, in which case the storage queues are included within this same network terminal as is stated in claim 2, or can be transmitted from two different terminals, in which case the storage queues are also belonging to two different network terminals as is stated in claim 3.
Another characteristic feature of the present invention is mentioned in claims 4 and 18.
The respective sets of parameters, associated to the respective storage queues, thereby include traffic and connection parameters associated to the respective bitstreams of which the data packets are stored within these queues, but also include a status parameter indicative of the status of these queues. As was stated by the previous claims 1 and 17, the grant rate associated to one queue, is then adapted based upon at least one parameter from both queue parameter sets. This implies that this queue grant rate may be solely dependent upon the status parameters, or solely on one of the traffic and connection parameters associated to both queues, or on a combination of both. In either case, the upstream data packet rate can be more efficiently controlled for matching the common transmission link capacity. Indeed, the traffic and connection parameters in general represent boundaries within which the actual traffic rates must lie. If the queue grant rate, which directly determines the corresponding upstream data transmission rate, is now dependent both on the own traffic limits, as well as on traffic limits of at least another, competing, bitstream, a better fit to the capacity of the upstream transmission link is obtained since a rate lying in between both boundaries will be the result.
In case only the status parameters are controlling the rate of the upstream transmission of the data packets, a medium access control method proportionally dividing the upstream link capacity amongst for instance the active bitstreams, thus for which the corresponding storage queues are not empty, is using that upstream link capacity in a much more efficient way than for instance the prior art system, which only took the requested bandwidth into account.
By combining the traffic and connection as well as the status parameters for determining the queue grant rate, it is evident that even a more optimal use of the upstream link capacity is obtained. Examples of such algorithms will be described into detail in a following paragraph of this document.
Yet a further characteristic feature of the present invention is mentioned in claims 5, 14 and 19.
In this way, the parameters associated to the respective queues are upstream transmitted by the network terminals themselves by means of upstream queue request messages. This upstream transmission is mandatory for the queue status parameters which can not be communicated to the medium access controller in another way. The traffic and connection parameters on the other hand can be incorporated within the same upstream queue request messages, as is for instance stated in claim 15, but can also be delivered to the medium access controller from for instance the central station where this information is centrally stored during the connection set-up phase.
Still another characteristic feature of the present invention is mentioned in claims 6 to 11 and 20 to 26.
By this, the queue grant rate, being directly related to the upstream associated packet transmission rate, is only adapted as long as the corresponding storage queue status parameter is complying with a predetermined criterion as is described by claims 6 and 20. In a previous paragraph such a criterion was already mentioned, namely that the queue should not be empty. Another criterion could be that at least a minimum number of cells are buffered in the storage queue. The storage queues of which the associated parameters are influencing the upstream packet transmission rate of one particular storage queue together constitute one group, whereas a subgroup of this group is formed by all storage queues from the group for which the status parameters fulfil this predetermined criterion. Claims 7 and 21 state that, in stead of using the status parameters extracted from the upstream request messages as such, first status related parameters are determined from them, after which step these status related parameters are then further used for determining the subgroup. The reason behind this latter solution is related to an eventual long delay between the arrival of two successive queue request messages. In this case downstream transmitted grants may already have caused a particular storage queue to be empty, a long time before the next request message with the indication of this new status has arrived. For these networks, the status related parameters are derived from the latest version of the received status parameters, but take already into account recently generated grants to this same storage queue. The thereby determined status related parameters thus aim at representing the actual status of the storage queues. In case however upstream request messages are arriving frequently enough to overcome this delay problem, there is no need for determining these status related parameters.
From the parameters associated to the storage queues of the subgroup, an excess bandwidth is then determined which will be proportionally divided amongst the storage queues of the subgroup. In case the group consists of the total of all storage queues within the network, and in case the grant rates associated to the storage queues for which the status parameters do not meet the predetermined criterion are set to zero, this excess bandwidth may correspond to an upstream bandwidth remaining available on the common transmission link when all bitstreams stored in the storage queues are already using the part determined by their traffic parameters, such as the peak cell rate or minimum cell rate. This excess bandwidth may be determined according to different methods, more details will be given in the descriptive part of this document. In addition, by proportionally dividing this excess bandwidth amongst these bitstreams of the subgroup, fairness amongst these competing bitstreams is obtained. This will also be explained into more detail in this descriptive part.
Still a further characteristic feature of the present invention is mentioned in claim 12.
Since the groups, the subgroups and the parameters may vary in time, the method is performed at particular predetermined instances, resulting in an adaptive method. These predetermined instances are for instance determined by the sending, at regular intervals of so-called PLOAM (Physical Layer Operation And Maintenance) cells, indicating to the network terminals that these are allowed to transmit their upstream request messages, as was also already the case for the prior art system.
The present invention relates as well to a central station including such a medium access controller as described by the above mentioned claims 19 to 26, as well as to a communications network including such a medium access controller and a network terminal as described in the above mentioned claims.